The high levels of methane or natural gas were detected by methane-measuring aircraft flying over the underground storage facility in Los Angeles. Southern California Gas (SoCalGas) had started refilling Aliso Canyon on Aug. 1.
The two aircraft flights on Aug. 3 and Aug. 17, detected what appears to be methane escaping from an unknown leak at the facility, although the volume of gas escaping is very low, the California Air Resources Board told Southern California Public Radio.
The methane levels exceeded the state limit of 250 kilograms per hour on those flights. At its peak, Aliso Canyon was leaking 35,000 kilograms per hour.
The investigation into the leak or leaks continues by the state and the company.
Aliso Canyon was the sight of the country’s biggest-ever methane leak in 2015-2016.
The facility is the largest natural gas storage facility in the West and can handle up to 86 billion cubic feet (Bcf) of natural gas. State officials have reduced that volume for increased safety.
The leak began on Oct. 23, 2015, and was contained on Feb.11, 2016. It is estimated 107,000 tons of methane and 8,000 tons of ethane escaped into the air. The cause of the leak remains under investigation.
The leak forced the evacuation of 8,000 residents.
SoCalGas paid a $4 million fine to resolve criminal charges. The utility faces additional lawsuits by state and county agencies. It also faces more than 100 civil lawsuits.